Carbon nanotubes have attracted considerable attention and generated intense research activities on nanotubes and their composites with polymers. The interest in this extraordinary carbon form is based on exceptional mechanical, electrical, and thermal properties. (Yu, M. F. et al., Phys. Rev. Lett. (2000), 84, 5552; Li, F. et al., Appl. Phys. Lett. (2000), 77, 3161; Wong, E. W., et al., Science (1997), 277, 1971; Kim, P., et al., Phys. Rev. Lett. (2001), 87, 215502.) These properties combined with the very high aspect ratio make nanotubes an excellent candidate for novel composite materials that can be used in a wide variety of transportation, aerospace, energy and electronics applications.
Several recent studies focus on the fabrication and characterization of carbon nanotube—polymer nanocomposites (Shaffer, M. S. et al., Adv. Mater. (1999), 11, 937; Qian, D. et al., Appl. Phys. Lett. (2000), 76, 2868; Ajayan, P. M. et al., Adv. Mater. (2000), 12, 750; Hadjiev, V. G. et al., Appl. Phys. Lett. (2001), 78, 3193; Haggenmueller, R. et al., Chem. Phys. Lett. (2000), 330, 219; Jin, L. et al., Appl Phys. Lett. (1998), 73, 1197; and Wood, J. R. et al., Comp. A (2001), 32, 391). For example, a solvent-evaporation method was applied for multiwall carbon nanotube-polystyrene composites with enhanced mechanical properties (Qian et al.). In this study, the modulus of a 1 weight percent (“wt %”) MWNT-polystyrene composite was within ˜10% of a theoretical prediction incorporating dispersion and effective load transfer parameters from the matrix to the nanotubes. In other studies, the orientation of nanotubes has been shown to influence the electrical, thermal, and mechanical properties of composite materials. For example, using 2-D X-ray diffraction to measure the alignment of nanotubes, Jin et al. showed that the full width at half maximum (FWHM) of a mechanically stretched 50 wt % MWNT-poly(hydroxy aminoether) composite was 46.4° (Id.). In another study involving the use of Raman spectroscopy, Wood et al. showed a correlation between deformation and alignment of a thermoset composite that was sheared before curing.
Although nanotube alignment influences various properties of composite materials, many of the various methods used to prepare these composites do not adequately disperse the carbon nanotubes. For example, melt mixing single walled carbon nanotubes (“SWNTs”) with polymer matrix materials in dry form leads to SWNT agglomerates that are difficult to disperse. Likewise, concentrated nanotube-polymer materials (“masterbatches”) typically contain agglomerated nanotubes that are also difficult to disperse using standard polymer melt processing techniques. Thus, there is a continuing need to provide composite materials and fibers having highly aligned and dispersed carbon nanotubes. There is also a continuing need to provide polymer composite materials and fibers having improved physical properties, such as having high thermal conductivities.